1. Field of the Invention
This invention relates to the manufacture of electronic devices such as integrated circuits. Particularly, this invention relates to improved semiconductor substrate materials, such as silicon wafers, used in the manufacture of integrated circuit devices. Specifically, this invention is directed to semiconductor substrate materials having enhanced ability for gettering deleterious impurities, contaminants and defects during device manufacture away from the region of device formation.
In the manufacture of integrated circuit devices on silicon wafers, the presence of and introduction of defects, contaminants and impurities on and near the device formation surface of the wafer creates excessive current leakages which greatly affects the yield of usable devices obtained. The art has recognized that the deleterious defects, contaminants and impurities can be to some extent relocated to non-harmful regions in the substrate material away from the device formation region. The methods and processes for diffusing and trapping the defects, contaminants and impurities away from the active device region both prior to and during device formation are termed gettering in the electronics industry and art.
2. Description of the Prior Art
Several techniques and processes for gettering in semiconductor materials to improve device yields have been disclosed in the art. Known gettering techniques and processes for semiconductor materials can be generally classified as based on external or internal means.
External gettering involves modifying the backside surface of the wafer to provide sites to which the defects, contaminants and impurities are attracted. A present commercially used external gettering technique is to introduce mechanical damage to the backside of the wafer. The mechanical damage is imparted to the backside of the wafer by scratching the surface or sanding or grinding with an abrasive means to alter the crystalline structure and impart imperfections which attract and trap defects, contaminants and impurities away from the active device region of the wafer. Although backside damaged wafers provide gettering, the damage to the wafer creates additional problems in fragility, handling and cleaning to remove particulates formed and the damaged area provides potential traps for holding fluids and materials employed in the device manufacturing process which can result in further wafer contamination. U.S. Pat. No. 4,144,099 describes wafer gettering by employing backside mechanical damage.
Another example of external gettering is described in U.S. Pat. No. 3,997,368 wherein a stressed layer of silicon nitride or aluminum oxide is formed on the backside of the wafer which is then annealed to cause stacking fault nucleation sites to diffuse to the backside. Still another example is described in U.S. Pat. No. 3,929,529 wherein a surface of the wafer is anodized to form a layer of porous silicon, the contaminants are diffused from the body of the wafer to the porous silicon and the porous silicon layer is then oxidized to silicon dioxide.
U.S. Pat. No. 4,053,335 discloses a means of external gettering in semiconductor materials by providing a layer of polysilicon on the backside of the wafer. The grain boundaries of the polysilicon provide sites for segregation of impurities from the substrate. As the polysilicon grain boundaries are not annealed out at high temperature, the gettering capabilities remain effective throughout high temperature processing used in device manufacture.
Other commonly employed external type gettering means utilize boron- or phosphorus-doped semiconductor materials, ion implantation, such as argon, or heavy diffusion of impurities, such as boron and phosphorus, into the substrate material. U.S. Pat. No. 3,874,936 provides a description of the latter technique.
More recently, the gettering effect of oxygen contained in the substrate material has been reported in "Solid State Technology", July 1981, pages 55-61, and is referred to as internal gettering. Oxygen is present in Czochralski grown silicon as it is introduced to the crystal from the dissolution of the quartz crucible employed to hold the silicon melt during crystal pulling. The precipitation of oxygen contained in the substrate material can form useful sites for gettering deleterious defects, contaminants and impurities.
With any gettering means, the active region of the substrate material where the devices are formed must be free of gettering sites. Thus, a zone about 10-25 microns and preferably about 15-20 microns in depth from the device surface of the wafer which is denuded of gettering sites must be created to prevent device yield loss from defect interference. The oxygen concentration in a substrate material can be reduced near the surface through outward diffusion at the process thermal conditions employed in device manufacture.
With the rapidly advancing device manufacturing technology and particularly with respect to complex and lengthy processing steps and increased circuit density and total circuit size on a wafer, it has become apparent improvements are needed in the gettering capabilities of substrates to cope with the increased requirements and provide effective gettering throughout the device processing steps in order to achieve an acceptable yield of good devices per wafer.